The invention relates to concrete mixers. More particularly, the invention is concerned with a concrete mixer of the type wherein a mixing drum tapers conically toward a fill and discharge opening; wherein a stub axle is secured to the drum bottom and journaled in a bearing on a vehicle frame for rotation on an axis which slants from the drum bottom upwardly relative to the horizontal toward the fill and discharge opening; wherein the inner wall of the mixing drum is provided with helical concrete conveying elements; and wherein the mixing drum contains an auxiliary coaxial mixing tool.
A transit concrete mixer of this general type has heretofore been known in which the mixing tool consists of a helix that is mounted in a fixed position within the mixing drum. The helix extends over about two-thirds of the length of the mixing drum, and at its end next to the drum bottom it is journaled on a stub shaft which is fixed to the drum bottom and projects into the core of the helix. At its other end the helix core is extended to project outward through the fill and discharge opening of the drum where it has an angled portion which is sustained on a mounting frame for the drum. The additional mixing effect which this helix produces is small. The production costs are high due to the mounting of the helix at both ends and the spreading of its axial length over a substantial portion of the drum length. The weight of the mixer is thereby considerably increased.
Also heretofore known has been a transit concrete mixer in which a substantially cylindrical mixing drum is rotatable on a horizontal axis. In that case the mixing drum has helical blades secured to its inner wall and it is provided with a coaxial supplemental helix. The supplemental helix is supported on an overhung shaft which extends through and is rotatably mounted on the drum bottom. The other end of the shaft is journaled in a spider secured within the drum. The supplemental helix extends over the main portion of the length of the mixing drum. The drum and the helix are rotated by a drive shaft which extends parallel to the drum wall; said drive shaft, on one hand, drives a pinion in mesh with a ring gear on the drum; and on the other hand, the drive shaft is connected by a chain drive with the helix supporting shaft at the end of the latter which projects from the drum bottom. This prior art mixer has the disadvantage that the long helix increases the production costs and also considerably increases the weight of the mixer. Moreover, the spider which supports the free end of the helix supporting shaft and which faces the discharge opening of the drum from the inside, interferes with the outward movement of the concrete through the discharge opening.